file.save: an explicit jpg format is refused too

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/cmd/file.rs

@@ -345,7 +345,7 @@ pub fn save_bytes(doc: &Presentation, format: &str) -> Result<Vec<u8>> {
         "rtf" => Ok(deckcraft_format::rtf::slides_to_rtf(doc).into_bytes()),
         "pdf" => deckcraft_pdf::export(doc, &Default::default()).map_err(|e| EngineError::Other(e.to_string())),
         "gif" => gif_bytes(doc, &Value::Null),
-        "png" | "jpeg" => Err(EngineError::Other("saving a presentation as a single image isn't supported; use file.export".into())),
+        "png" | "jpeg" | "jpg" => Err(EngineError::Other("saving a presentation as a single image isn't supported; use file.export".into())),
         _ => deckcraft_format::save(doc).map_err(|e| EngineError::Other(e.to_string())),
     }
 }